It is known to provide a decoupler mechanism on an accessory, such as an alternator, that is driven by a belt from the crankshaft of an engine in a vehicle. Such a decoupling mechanism, which may be referred to as a decoupler assembly or a decoupler, permits the associated accessory to operate temporarily at a speed that is different than the speed of the belt. As is known, the crankshaft undergoes cycles of accelerations and decelerations associated with the firing of the cylinders in the engine. The decoupler permits the alternator shaft to rotate at a relatively constant speed even though the crankshaft from the engine, and hence, the pulley of the decoupler, will be subjected to these same cycles of decelerations and accelerations, commonly referred to as rotary torsional vibrations, or torsionals.
It has been found also that the alternator itself can contribute to torsional vibrations due to clipping of the field voltage that can take place during operation of the alternator. When such torsionals occur at certain frequencies, they can result in resonance in the spring of the decoupler, leading to large angular swings of the decoupler pulley relative to the hub, which ultimately leads to failure of the decoupler spring from fatigue.
In situations where torsionals are problematic, it has been found that damping of the movement of the decoupler pulley and hub relative to one another can extend the life of the spring. However, it has also been found difficult to manufacture the decoupler in such a way that it remains compact, while ensuring that the tolerance stack up associated with its manufacture does not result in large variability in the amount of damping that is provided. If too little damping is provided, the resonance in the spring may not be sufficiently diminished to keep the spring from failing prematurely. If too much damping is provided, then the driven accessories on the engine may not be sufficiently isolated from the torsionals that occur at the crankshaft.
It would be beneficial to provide a decoupler that addresses these issues.